Acoustic sensor detects weak magnetic fields without an external bias magnet
Carefully oriented magnetic layers let an acoustic-wave sensor detect weak fields without an external bias magnet. The peer-reviewed laboratory experiment measured both sensitivity and directional response. Its two layered designs use internal magnetic alignment to simplify the measuring arrangement, while electrical excitation and readout still power the device’s acoustic waves.
Science··Night
Layer alignment replaces an external bias magnet
Careful alignment of magnetic layers allowed two experimental sensors to measure fields without a separate bias magnet. The peer-reviewed study compares a scissor-like arrangement of magnetic directions with a design in which both layers tilt the same way. This internal alignment supplies the magnetic bias during measurement, reducing the need for a separate magnet or a field-generating coil. Electrical power still excites and reads the acoustic waves.[1]
A magnetic film changes the travelling wave
Input and output transducers send waves across a quartz surface, through a magnetic film placed between them. An applied magnetic field changes the film’s elastic properties, altering wave speed and the phase measured at the output. A silicon dioxide guiding layer keeps acoustic energy close to the surface. The multilayer film combines iron, cobalt, silicon and boron with nickel–iron and manganese–iridium layers.[1]
Weak-field sensitivity comes with a directional response
The lowest detection threshold was measured at 100 hertz: 22 picotesla per square-root hertz. At a frequency of 10 hertz, the threshold was 69 in the same units. The angular response followed an approximately sinusoidal, two-lobed pattern as each device completed a full rotation. Measurements after magnetic saturation in opposite directions retained small differences linked to magnetic history. The results characterize laboratory sensors; diagnostic performance and mass production were outside the demonstration.[1]
